It looks like the problem here might be your usage of theConnectedMonitor option. That option should only be used to tell the driver about a display device that it cannot detect on its own (such as when using a KVM). Are both of your displays directly connected to the videocard from bootup, or are you using a KVM, or some other intermediary device?

I'd suggest removing both instances of that option from your X configuration. If that fails to help, please start X with the following command:
startx -- -logverbose 5

I have two LCD displays, a 24" and a 17".
The 24" is connected using DVI on the first card's first output.
The 17" is connected using a DVI to VGA adapter on the first card's second output.

If I remove the ConnectedMonitor options both screens are used, but the 24" is initialized as the second screen. This is annoying because then applications go fullscreen on the 17" (I could live with that, but watching DVDs on the 17" while the 24" displays xclock and mails makes me want to cry )

Attached is a nvidia-bug-report generated with the "swaped screens" problem and -logverbose 5.

When assigning display devices to X screens, the NVIDIA X driver by
default assigns display devices in the order they are found (looking first
at CRTs, then at DFPs, and finally at TVs). This option can be used to
override this assignment. For example, if both a CRT and a DFP are
connected, you could specify:

Option "UseDisplayDevice" "DFP"

to make the X screen use the DFP, even though it would have used a CRT by
default.

Note the subtle difference between this option and the "ConnectedMonitor"
option: the "ConnectedMonitor" option overrides what display devices are
actually detected, while the "UseDisplayDevice" option controls which of
the detected display devices will be used on this X screen.

Which is exactly the answer to my problem

Thanks again for the great support !

P.S. : those drivers just rock, every single issue I ever had with nvidia/linux seems resolved (xv vsync !)